Thermoplastic Systems Research Articles

Comparison of low-velocity impact damage in laminated composites for two thermoplastic material systems

Aircraft manufacturers are investigating thermoplastic material systems to produce parts more quickly and efficiently. Detailed damage data is needed to evaluate existing damage analysis methods, developed for thermoset materials, to predict damage in thermoplastic materials. Damage maps were created for two thermoplastic material systems subjected to low-velocity impact over a range of impact energies. In this paper, the damage maps were used to investigate and compare the damage response of the different material systems. Impact specimens were manufactured from TC1225 LMPAEK T700G from Toray Industries and APC AS4D/PEKK-FC from Solvay. The effect of the degree of crystallinity on the damage response was also investigated using a third set of specimens manufactured using the Toray material and a quenching process. Using a combination of data obtained from X-ray computed tomography and ultrasonic testing, damage maps were created for every interface and ply for selected specimens showing matrix cracks, delamination outlines, and fractured fibers. The LMPAEK specimens were found to have fewer and smaller delaminations than the PEKK specimens for impacts at the same energy. However, the LMPAEK specimens contained a larger number of fiber breaks. A similar trend was observed when comparing low-crystallinity LMPAEK specimens with the baseline LMPAEK specimens. The LMPAEK specimens often contained lines of fiber fractures in near-surface plies emanating from the contact region that were not present in the PEKK specimens. The different damage responses may indicate that the material selection will be a function of the application and loading.

An evaluation of progressive damage analysis methods for modeling low velocity impact of thermoplastic composites

State-of-the-art progressive damage and failure analysis (PDFA) tools for composites were developed for thermoset materials because of the prevalence of the material system within the aerospace industry and the need to address damage growth behavior of composites analytically. As the presence of thermoplastic materials has started to grow in the industry, it is necessary to be able to predict their behavior as well. However, it is unclear whether existing tools based on linear elastic fracture mechanics (LEFM) can be used to represent thermoplastics. One application area for PDFA tools is low velocity impact (LVI). This work presents two PDFA modeling methods originally validated for predicting damage of thermoset composites in low-velocity impact and evaluates their ability to model a thermoplastic material system in the same scenario. Both methods use MAT299, a continuum damage mechanics material model, to represent interlaminar damage and a cohesive tiebreak definition within LS-DYNA to represent delamination within a laminate. The results reveal that the cohesive tiebreak modeling method, while successful in modeling thermoset materials, is not currently capable of predicting the delamination response of thermoplastics. The larger strain energy release rates for the thermoplastic material in combination with a deficiency in the modeling method are believed to be the cause of the reduced delamination in the simulations. Potential routes for improving the delamination prediction in the simulations include adjusting the mode-mixity behavior, using a different cohesive approach for delamination, developing new best practices for cohesive behavior, and incorporating further non-linearity into the material model.

Ultra-high-rate Manufacturing of Thermoplastic Window Plug using Hybrid Overmolding

Highly loaded complex parts are machined from a solid block of metal by removing material through cutting, boring, drilling, and grinding to obtain the three-dimensional shape. Most cases, this involves removing as much as 80 percent of the material from a billet, which is time-consuming and inefficient considering the cost of the materials. Alternatively, these complex parts can be manufactured using hybrid overmolding process which involves injecting plastics over a reinforced substrate with continuous fiber-reinforcement eliminating subtractive machining or joining of multiple parts. The substrate is typically heated using an infrared (IR) oven and preformed over a solid mold to a three-dimensional shape using thermoforming. Injection overmolding material can also be reinforced with discontinuous fibers based on the design requirements. Both thermoforming and injection molding are matured automotive ultra-high-rate manufacturing processes. Adopting these technologies to aerospace requires advanced aerospace-grade thermoplastic material systems and developing the hybrid overmolding process that combines both thermoforming and injection molding processes. Material compatibility is one of the key enablers for the fusion across the overmolded interfaces. To demonstrate the overmolding technology for an aerospace application, Victrex AE250 low-melt polyaryletherketone (LM-PAEK) system reinforced with AS4 fibers and a 30% carbon fiber-reinforced polyetheretherketone (PEEK) were used to overmold aircraft window plugs to be used for cargo conversion of passenger aircraft. The fully automated overmolding process was demonstrated using KraussMaffei multi-robotic thermoforming and injection molding system. Thermal and mechanical test evaluations were employed to assess the material compatibility and overall part quality. Photomicrographs and flexure tests conducted on test samples extracted from the window plugs indicated satisfactory fusion across the overmolded interface and optimized holding of PEEK materials.

Regulation of the Phase Structure in the Crystallizing Curing System PCL–DGEBA

Qualitative and quantitative aspects of the formation of various types of phase structures, sizes and compositions were considered. For the studied polycaprolactone–epoxy resin/4,4′-diaminediphenylsulfone system, a phase diagram characterized by amorphous separation with a lower critical solution temperature was constructed and its evolution was traced with increasing conversion degree of epoxy groups. A method is proposed for determining the temperature–concentration parameters that determine the type of phase structure of composite materials, based on the optical interferometry method. All types of phase structures and features of structure formation in the phase reversal region and at its boundaries have been studied using optical and scanning electron microscopy methods. The dimensions of the structural elements were determined and their correlation with the temperature and concentration regimes of the system’s curing was established. The composition of phases in cured compositions was studied using FTIR spectroscopy, DSC and scanning electron microscopy. It is shown that by varying the temperature–concentration parameters of curing reactive thermoplastic systems, it is possible to specifically regulate the type of phase structure, phase sizes and their composition, which determine the operational properties of the material.

Effect of High Fiber Content on Properties and Performance of CFRTP Composites

Continuously reinforced thermoplastic composites are widely used in structural applications due to their toughness, light weight, and shorter process cycle. Moreover, they provide flexibility in design and material selection. Unlike thermoset composites, continuous fiber content to maximize mechanical properties in thermoplastic composites has not been well investigated. In this paper, three thermoplastic systems are investigated to study the optimum content of continuous fiber reinforcement. These systems include carbon fiber/polyphenylene sulfide (PPS), glass fiber/PPS, and glass fiber/high-density polyethylene (HDPE). Tapes were made at several fiber contents, and samples were compression molded and tested using thermo-gravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), tensile, 3-point flexure, and short-beam shear tests. Results revealed that higher fiber content led to an increase in the glass transition and melt transition temperatures of the polymer. Some mechanical properties increased with fiber content and then began to decrease upon further addition of fibers, while other properties, such as ductility and interfacial bond strength, decreased with more reinforcement. Furthermore, the optimum fiber contents to maximize mechanical properties are different for different properties and different materials.

Comparative Environmental Life Cycle Assessment on Corn Starch Plasticization and Co-Plasticization Processes

Starch has overtaken the bioplastic market in developing thermoplastic starch-based blends and composite systems owing to its biodegradability and sustainability. Thermoplastic starch (TPS) development is mostly a two-stage process involving plasticizing starch and blending plasticized starch with a polymer. Most of the research focuses on improving the properties of the blend system through different methodologies, including various plasticizers and co-plasticizers. However, limited studies have analyzed the environmental effects of plasticizers or co-plasticizers and their processing. Thus, in this research, the environmental impact of starch plasticization processes performed by co-plasticization (glycerol–urea, glycerol–citric acid, and glycerol–succinic anhydride) and by conventional glycerol-based plasticization is compared through life cycle assessment (LCA). The results showed that glycerol–citric acid- and glycerol–succinic anhydride-based co-plasticization had a comparable environmental impact to traditional glycerol-based plasticization. In contrast, the glycerol–urea-based co-plasticization process exhibited the highest effect on the environment. Furthermore, to reduce the environmental impact, a sensitivity analysis of the plasticization processes was conducted by changing the energy aspect of the processes through quantitative and qualitative approaches. The qualitative approach significantly reduced major impact categories such as global warming, carcinogens, ecotoxicity, and fossil fuel depletion.

Mechanical Assessment of Denture Polymers Processing Technologies.

Removable prostheses have seen a fundamental change recently because of advances in polymer materials, allowing improved durability and performance. Despite these advancements, notable differences still occur amongst various polymer materials and processing technologies, requiring a thorough grasp of their mechanical, physical, and therapeutic implications. The compressive strength of dentures manufactured using various technologies will be investigated. Traditional, injection molding, and additive and subtractive CAD/CAM processing techniques, all utilizing Polymethyl methacrylate (PMMA) as the main material, were used to construct complete dentures. The specimens underwent a compressive mechanical test, which reveals the differences in compressive strength. All the specimens broke under the influence of a certain force, rather than yielding through flow, as is characteristic for plastic materials. For each specimen, the maximum force (N) was recorded, as well as the breaking energy. The mean force required to break the dentures for each processing technology is as follows: 4.54 kN for traditional packing-press technique, 17.92 kN for the injection molding technique, 1.51 kN for the additive CAD/CAM dentures, and 5.9 kN for the subtractive CAD/CAM dentures. The best results were obtained in the case of the thermoplastic injection system and the worst results were recorded in the case of 3D printed samples. Another important aspect depicted is the standard deviation for each group, which reveal a relatively unstable property for the thermoplastic injected dentures. Good results here in terms of absolute property and stability of the property can be conferred to CAD/CAM milled group.

Influence of viscoelastic behavior in flame retardancy of thermoplastic starch multicomponent systems loaded with leather waste

Influence of viscoelastic behavior in flame retardancy of thermoplastic starch multicomponent systems loaded with leather waste

Environmental Durability of Bio-Based and Synthetic Thermoplastic Composites in Large-Format Additive Manufacturing.

This research investigates the durability of large-format 3D-printed thermoplastic composite material systems under environmental exposure conditions of moisture and freeze-thaw. Durability was evaluated for two bio-based composite material systems, namely wood-fiber-reinforced semi-crystalline polylactic acid (WF/PLA) and wood-fiber-reinforced amorphous polylactic acid (WF/aPLA), and one conventionally used synthetic material system, namely short-carbon-fiber-reinforced acrylonitrile butadiene styrene (CF/ABS). The moisture absorption, coefficient of moisture expansion, and reduction of relevant mechanical properties-flexural strength and flexural modulus-after accelerated exposure were experimentally characterized. The results showed that the large-format 3D-printed parts made from bio-based thermoplastic polymer composites, compared to conventional polymer composites, were more susceptible to moisture and freeze-thaw exposure, with higher moisture absorption and greater reductions in mechanical properties.

Acrylonitrile‐butadiene‐lignin thermoplastic rubber adhesive for enhanced metal‐to‐metal joining

AbstractWith the growing requirement for lightweight structural materials in automotive, aerospace, and infrastructure applications, multi‐material joints made with adhesive have attracted intense research interest. Commercial thermoset adhesives are one‐time cures, and difficult to disassemble the bonded components for repair and recycling. Our prior work with a thermoplastic acrylonitrile‐butadiene‐lignin rubber (ABL) addresses this sustainability/recycling challenge, but the adhesive exhibits deficient joining strength compared to standard thermosets. Here, we modify the ABL matrix by loading particulate fillers to enhance its modulus and toughness. The goal is to manufacture a cure‐free thermoplastic adhesive system with a simple dispensing protocol and characteristic ductility combined with a high yield stress for improved shear strength of a bonded joint. Fumed silica (FS) and epoxidized glass spheres (EGS) were used as fillers in the ABL to promote the dispersion of lignin particles that tailored the functionalities and free energy components of the adhesive surface. With optimal loading of FS (5 wt%) and EGS (30 wt%) in the ABL adhesive matrix, the lap‐shear strength of the bonded aluminum joint was elevated by 128%, compared to the neat ABL, reaching 21 MPa, which is 90% of the performance of a commercial epoxy‐based adhesive.Highlights A partly renewable filler‐toughened thermoplastic adhesive has been developed. This thermoplastic gives nearly equivalent performance of adhesively bonded aluminum joint compared to standard thermosets. Experimental and simulation data help understand the adhesive reinforcing mechanism by the fillers.

Design of Unplasticized Polyamide 12 Oilfield Line Pipe Based on Published Regression Curves and ASTM F3524

The long-term strength of unplasticized polyamide 12 (PA-U12) has been characterized using standard methods for plastic pressure pipe during the qualification process for use in buried piping systems for natural gas delivery operating at low ambient temperatures, usually less than 20 to 30°C at pressures previously served only by steel pipe. The high strength characteristics of the material also made it interesting as a steel substitute for buried and above-ground industrial pressure pipe applications. So far, typical geometries are diameters up to 6 inch (162 mm) with wall thicknesses up to DR9. Assuming a design factor of 0.63 applied to the PPI TR-4 listed HDB, DR9 PA-U12 pipes have a maximum pressure at 23°C of 496 psig (3.4 MPa), although design pressures will typically be lower. These industrial systems can operate at much higher temperatures, up to ~ 50°C for above-ground installations in pipe supports or up to ~ 65°C for surface-laid oilfield pipes. Design engineers need the temperature dependent strength curves to properly design a thermoplastic pressure piping system. Therefore, the regression curves have been extended by LTHS tests up to 120°C. Corresponding test durations enabled to define the location of knees with determination of second branches. These branches are caused by hydrolytic degradation of the polymer resulting in brittleness of the polyamide after long times at elevated temperature in sufficiently wet environments or services. The first appearance of a knee is at 60° C and approximately 44 years. This paper describes various standards to which PA-U line pipe and materials must conform, and the development of standardized, temperature dependent, long-term strength reference curves for PA-U12 pressure pipe, including the transition from ductile to brittle behavior at long times and high temperatures. These curves have been standardized first in DVS and followed by ISO based on the combined LTHS data of pipes made from two different PA-U12 180 compounds and one PA-U11 180 compound. An example of a typical PA-U12 180 pipe design is presented, applying chemical resistance derating factors for oil and gas applications in the design process. Short Summary: Oilfield pipeline design engineers need temperature dependent strength curves to properly design a thermoplastic pressure piping system for use at temperatures often far above the typical range for natural gas distribution. Therefore, LTHS regression curves have been experimentally developed at temperatures up to 120°C to define the location of knees and characterization of second branches. In this paper we describe various standards to which PA-U line pipe and materials must conform, and the development of standardized, temperature dependent, long-term strength reference curves for PA-U12 pressure pipe, including the transition from ductile to brittle behavior at long times and high temperatures. These curves have been standardized in ISO and DVS and apply to both PA-U12 and PA-U11 [1,2]. For PA-U12 line pipe we also present an example for a typical pipe design, where chemical resistance derating factors are applied for oil and gas applications in the design process.

Multi-stage, in-situ polymerisation for low-exotherm, liquid resin infusion of thick thermoplastic laminates at room temperature

This study exploits the unique attributes of a reactive thermoplastic acrylic resin system (room-temperature liquid-resin infusibility, in-situ polymerisability, and room-temperature weldability) to achieve additive-free mitigation of exothermic heat generation during thick laminate production. Additives are typically required when thicknesses exceed 12 mm, but their use often compromises the degree of polymerisation and mechanical performance. An innovative multi-stage manufacturing scheme has been used to achieve a 55 °C reduction in exothermic peak temperature during the production of a 16-mm-thick laminate compared to the use of a standard resin infusion (89 °C) for the same thickness. Laminates produced using the multi-stage scheme were also found to exhibit 24 % higher short-beam shear strengths than those obtained via standard resin infusion, suggesting improved part quality as an additional benefit. Further demonstrating the applicability of the proposed method, a 40-mm-thick laminate was successfully produced with a peak temperature of only 60 °C. This work highlights the potential of room-temperature welding for practical and low-cost production of ultra-thick laminates at room temperature.

Fabrication of double layer nanoparticle infused starch-based thermoplastic food packaging system for meat preservation

The current work aims to produce nanoparticle-infused starch-based bioactive thermoplastic packaging films. The FeO and ZnO nanoparticles were examined to be potential active ingredients for the production of nanoparticle-infused bioactive thermoplastic packaging films. The bio-thermoplastic films infused with FeO and ZnO nanoparticles showed high oxygen scavenging and antimicrobial activity, respectively. Consecutively, both films were combined to form a double-layer Nano-Biothermoplastic packaging system for food preservation. The distribution and diffusion of nanoparticles in starch-based films were examined to be influenced by the amorphous character of starch and the swelling index of the film, respectively. The amorphous property of starch molecules showed a masking effect on the crystalline characteristics of nanoparticles in Nano-Biothermoplastic films. The diffusion of nanoparticles from the Nano-Biothermoplastic packaging system was found to influence the microbial, chemical, and color characteristics of mutton and chicken meat stored at 4 °C.

Ultrasonication optimisation and microstructural characterisation for 3D nanoparticle dispersion in thermoplastic and thermosetting polymers

3D nanoparticles are important as reinforcing or functional phase in polymer composite materials; however, an optimised deagglomeration and uniform distribution of these particles is required to fully exploit their nanoscale properties. Classical dispersion methods like shear mixing have proven insufficient, and high-energy ultrasonication, as the preferred deagglomeration method, requires a challenging system-specific optimisation procedure. Therefore, a study was set up to reveal general scaling trends and good practices in developing an ultrasonication procedure for both thermoplastic and thermoset polymer-nanoparticle systems. The ultrasound energy density served as a universal scaling parameter and the higher power densities in the range of 1W/ml achieved by sonotrode ultrasonication were demonstrated to be necessary for complete deagglomeration. For epoxy and barium titanate (BaTiO3) as a below-percolation thermoset model system, an optimal energy density of 120 J/g was observed. Polyvinylidene difluoride (PVDF) and titanium carbonitride (TiCN) were selected as an above-percolation model thermoplastic system for which ultrasonication in suspension at an energy density of 950 J/ml followed by a crucial rotary evaporation step was necessary. X-ray computed tomography imaging has proven to be a powerful characterisation tool in combination with the matrix-free path diameter. This parameter was proposed as a novel parameter for single-parameter quantification of particle dispersibility as opposed to the commonly used and often inconclusive average cluster diameter.

A rule of mixtures approach for delamination damage analysis in composite materials

The present study aims at investigating the delamination behavior of laminated composites in different loading modes within a homogenization theory of mixtures. The delamination damage phenomenon is introduced at the bulk level by eliminating the explicit representation of interfaces. Potential delamination planes are identified according to the developed interfacial stresses, and damage evolution is computed for each mode independently through a stress-based formulation. An arc-length strategy is employed to solve equilibrium equations owing to the snap-back effects. Reliability of the adopted mixing theory, as a framework for integrating the delamination theory into, is assessed by comparing the results with the ones obtained from micromechanical models in a fiber metal laminate structure. Considering delamination, a good agreement is observed in mode I, mode II and mixed mode configurations by evaluating the results against available numerical and experimental data in thermoset and thermoplastic composite systems. The present method has the capability to be used in the conventional finite element codes with the number of elements kinematically needed in the thickness, regardless of the number of layers, which dramatically reduces the computational cost in modeling composites with large number of layers. The proposed approach is not intended to replace other exact methods at the coupon scale, however, its main application would be in modeling delamination on large scale systems with minimum loss of accuracy.

Thermoplastic waste segregation classification system using deep learning techniques

Thermoplastic waste segregation classification system using deep learning techniques

Engineered polysaccharide alpha‐1,3‐glucan in highly filled thermoplastic polyurethane systems

AbstractThis study explores the use of α‐1,3‐glucan, which can be produced through an enzymatic polymerization process, as additive for thermoplastic polyurethane composite systems. Most importantly, highly filled thermoplastic polyurethane composites can be achieved with up to 80% by weight polysaccharide content. Analysis of mechanical properties demonstrates that strength and modulus can be significantly improved, while the plasticizer content allows for adjustments of compound flexibility. The addition of 60% α‐1,3‐glucan increased the flexural modulus of the thermoplastic polyurethane by 497% while adding 80% α‐1,3‐glucan increased the flexural modulus by 3193%. Citrate esters can be incorporated as plasticizer to improve processibility and flexibility of the compounds. An increase in impact strength of 55% was achieved when 10% of tributyl citrate was added to the 80% α‐1,3‐glucan composite. Based on the compatibility and property enhancements, the use of these engineered polysaccharides may provide additional options for producing sustainable composite materials with high renewable content and unique properties.

Infusible thermoplastic composites for wind turbine blade manufacturing: Static characterization of thermoplastic laminates under ambient conditions

The necessity for recyclable materials in wind energy applications has fueled research in glass fiber reinforced thermoplastic composites to replace their thermoset counterparts. Toward demonstrating that infusible acrylic resins can replace epoxy based composite systems in wind blade manufacturing, comprehensive static test protocols were performed, and the resulting data are presented. Specifically, unidirectional and biaxial (±45) continuous E-glass reinforced thermoplastic and epoxy laminates were prepared in four and eight ply laminates. Physical properties were characterized including density, fiber volume fraction, and glass transition temperatures, together with mechanical properties for tensile, compression, and shear responses. Comprehensive evaluation of these data supports infusible acrylic thermoplastic resin systems as viable alternative prospects to replace epoxies in E-glass reinforced wind blades as verified by comparable results for both composite systems.

Approaching Polycarbonate as an LFT-D Material: Processing and Mechanical Properties.

Long-fiber thermoplastic (LFT) materials compounded via the direct LFT (LFT-D) process are very versatile composites in which polymers and continuous reinforcement fiber can be combined in almost any way. Polycarbonate (PC) as an amorphous thermoplastic matrix system reinforced with glass fibers (GFs) is a promising addition regarding the current development needs, for example battery enclosures for electromobility. Two approaches to the processing and compression molding of PC GF LFT-D materials with various parameter combinations of screw speed and fiber rovings are presented. The resulting fiber lengths averaged around 0.5 mm for all settings. The tensile, bending, Charpy, and impact properties were characterized and discussed in detail. Special attention to the characteristic charge and flow area formed by compression molding of LFT-D materials, as well as sample orientation was given. The tensile modulus was 10 GPa, while the strength surpassed 125 MPa. The flexural modulus can reach up to 11 GPa, and the flexural strength reached up to 216 MPa. PC GF LFT-D is a viable addition to the LFT-D process, exhibiting good mechanical properties and stable processability.

Hydrogen permeability of thermoplastic composites and liner systems for future mobility applications

High pressure hydrogen permeation tests were carried out and specific permeation rates of various thermoplastic matrix materials have been measured as well as of continuous fiber reinforced thermoplastic composites (PA6, PA12, PA410, PPA, PPS), considering non-crimp and crimp textile architectures. Furthermore, liners based on thermoplastic high barrier films made of EVOH were applied on PA6 composites and their effect on permeation rate were investigated. All samples were accompanied by pressure tightness tests and micrographs to determine manufacturing effects, microstructure, porosity and additional defects like microcracks. Experiments show that thermoplastic composites can reach low permeation rate as long as a damage-free microstructure is ensured. Furthermore, the influence of the matrix material can be assessed, whereby the influence of the textile architecture can only be roughly estimated and is considered to be small. EVOH layers show remarkable barrier properties and are easy to integrate into the composite structure.